Island



(No Model.)

J. O. TAFT.

MANUFACTURE OF TWIST DRILLS.

PatentedJpne 24, 1890.

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4 5 2 LIL WM WM Wow /%A UNITED STATES JEROME O. TAF I, OF PROVIDENGE RIIODE ISLAND.

PATENT OEEICEQ.v

MANUFACTURE OF TWIST-DRILL'S.

SPECIFICATION forming part of Letters Patent No. 430,792, dated June 24, 1890.

Application filed March 4, 1890. Serial No. 342,609. (No model.)

To all whom it may concern.-

Be it known that I, JEROME O. TAFT, a citizen of the United States, residing at Providence, in the State of Rhode Island, have invented a new and useful Improvement in the Manufacture of Twist-Drills, of which the fol lowing is a specification.

My invention relates to the manufacture of twist-drills by first forming opposite longitudinal grooves in the drill-blank,a11d then twisting the same to spiral form; and my invention consists in first forming the opposite longitudinal clearing-grooves with opposite longitudinally flattened or depressed surfaces between them, then twisting the grooved blank to spiral form, and then compressing the metal at the cutting corner or edge of the grooves to improve the quality of the drill and reduce the same to a uniform diameter, as hereinafter fully set forth.

Figure 1 represents a side elevation of the drill-blank at a stage in the manufacture of the same at which the straight clearinggrooves and the intervening flattened or depressed surfaces have been formed. Fig. 2 represents an enlarged cross-section taken in the line 0050 of Fig. 1. Fig. 3 represents a subsequent stage in the manufacture at which the grooved drill-blank shown in Fig. 2 has been twisted so as to impart a spiral form to the clearing grooves and intervening fiattened or depressed surfaces. Fig. 4 represents an enlarged cross-section taken in the line 00 at of Fig. Fig. 5 represents a side view of the finished drill provided with the compressed cutting corners or edges according to my improvement. Fig. 6 represents an enlarged cross-section taken in the line of Fig. 5.

In the accompanying drawings, A, Fig. 1, represents a drill-blank as heretofore employed in the manufacture of twist-drills, the said blank being provided with the straight longitudinal clearing-grooves ac and the intervening flattened or depressed surfaces b Z), as shown in the enlarged cross-section, Fig. 2,

and A, Fig. 3, represents the drill-blank A when the same has been twisted so as to impart the required spiral form to the grooves a a and the intervening surfaces Z) Z).

The twisting of the drill-blanks when of small and medium size is commonly performed without the application of heat, and in that case the metal at the cutting corners or edges 0 c of the clearing-grooves will be deteriorated by the stretching tension to which it has been subjected in the operation of twisting; and it is the object of my improvement to restore the original quality of the metal at the said cutting-corners, and I accomplish this result by compressing the said corners in suitable dies or between suitably-grooved rolls, whereby the metal at the cutting corner or edge 0 will be compacted, as shown in Fig. 6, thus improving the lasting qualities of the cutting-corner of the drill, and at the same time reducing the drill to the proper standard size.

I claim as my invention- The method of making twist-drills, which consists in first providing the blank with opposite longitudinal clearinggrooves having opposite longitudinally flattened or depressed surfaces between them, then twisting the grooved blank to spiral form, and then compressing the metal at the cutting corner or edge of the spiral grooves, as set forth.

JEROME C. TAFT.

'Witnesses:

, J OHN S. LYNoH,

SOOEATES SGHOLEIELD. 

